Method in the analysis of gases



Nov. 25, 1969 E. R. RYHAGE 3,479,798

mswon IN THE ANALYSIS OF GASES Filed April 16, 1965 INVENTOR E fi/K RA G/VAR RYHAGE BY M 701202, 77M

7% ATTO 5Z5 United States Patent 0 M 3,479,798 METHOD IN THE ANALYSIS OF GASES Erik Ragnar Ryliage, Armfeltsgatan 5, Stockholm, Sweden Filed Apr. 16, 1965, Ser. No. 448,701 Claims priority, application Sweden, Apr. 21, 1964, 4,911/64; Apr. 23, 1964, 5,025/64; Sept. 25, 1964,

Int. Cl. 301d 13/02 US. Cl. 55-158 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method in the analysis of gases and vaporized substances by means of a mass spectrometer connected to a gas chromatograph. More particularly, the invention relates to a method for separating the carrier gas from the gas mixture issuing from the'gas chromatograph in order to remove as much as possible of the carrier gas from the carried gas before the latter is introduced into the mass spectrometer.

The combination of a mass spectrometer and a gas chromatograph has proved a valuable tool for the analysis of gas mixtures and particularly mixtures of volatile organic compounds. However, the presence of the carrier gas, e.g. helium or hydrogen, in the gas mixture, while necessary in the gas chromatograph, is objectionable in the mass spectrometer. If the carrier gas is allowed to enter the ionization chamber of the mass spectrometer it is ionized along with the gases to be analysed, provided that normal ionization potentials are used, and the ions produced from the carrier gas may form the major part of the total ion current, so that the measurement of the ion current produced from the gases to be analysed is made impossible or uncertain.

Various means and methods have been devised to eliminate the adverse efiect of the presence of the carrier gas in the mass spectrometer, but even though such method and means are provided, the amount of carrier gas entering the mass spectrometer should be reduced to a minimum. A known method of achieving this end is based upon the fact that if a gas stream containing molecules or atoms of different weights is caused to expand, the lighter particles will collect in the peripheral parts of the stream while the heavier particles concentrate at the central part of the stream. Since the molecular weight of the carrier gas used in gas chromatography is consid: erably lower than that of the gases to be analysed, it is thus possible to separate the carrier gas from the gas mixture issuing from the gas chromatograph column by expanding the gas stream and providing an apertured diaphragm in the path of the expanded gas stream, the aperture having such size that it admits passage of the central portion of the stream only. The central portion which for the most part consists of the gas or gases to be analysed, is passed to the mass spectrometer, while the peripheral portion of the stream, which for the most part consists of the carrier gas, is deflected by the diaphragm and withdrawn from the system by some suitable means. However, this method suffers from the drawback 3,479,798 Patented Nov. 25, 1969 that either an insufficient amount of the carrier gas is removed or a relatively large amount of the carried gas is removed as well.

It is an object of the present invention to provide a method by which the carrier gas can be effectively separated from the gas mixture without any considerable loss of the carried substances.

According to the invention the mixture of carrier gas and carried substances issuing from the gas chromatograph is passed through a channel which is surrounded by a permeable material whose permeability to the carrier gas is considerably larger than its permeability to the carried substances. When the gas mixture is passing along this channel the carrier gas to a large extent diffuses through the surrounding material so that the gas arriving at the exit end of the channel contains little or no carrier gas. From the exit end of the channel the gas is passed on to the inlet of the mass spectrometer.

The material surrounding the said channel is formed into a tube-shaped body, and this body should be enclosed in a chamber provided with means for keeping the pressure outside the body at a lower value than the pressure in said channel in order to accelerate the diffusion of the carrier gas through the material.

The material used for separating the carrier gas from the carried substances may be such that it is permeable only to gases having very light molecules as for instance hydrogen and helium, while it is completely impermeable to gases having larger molecules. Certain metals, for instance gold, platinum and other metals belonging to the platinum group, and particularly palladium, in the form of thin sheets have this property and may be used for the purpose of the invention.

However, preferably the permeable material surrounding the gas fiow channel consists of porous or microporous material such as glass and similar inorganic thermoplastic materials, organic thermoplastic materials, ceramic materials, or porous metallic materials. The choice of material is determined by the required pore size, and this may vary within wide limits depending on the carrier gas to be used and the kind of substances to be analysed and also upon temperature and pressure and the velocity of the gas stream. Thus, in some instances the required pore size may be as large as 0.1 mm. and in other instances less than l0 mm., but usually the pore size should be between 10* and l()- mm. Thermoplastic organic and inorganic materials and ceramic material with mediumsized and large pores as well as porous metallic materials with relatively large pores are available on themarket. Materials having very fine pores can be made from a metal alloy by dissolving one of its constituents, the remaining constituents forming a porous material.

An apparatus for carrying out the invention will now be described with reference to the accompanying drawing which shows a longitudinal section of a tubing'connecting a gas chromatograph with a mass spectrometer. The gas chromatograph and the mass spectrometer may be of any conventional types and are not shown.

Referring now to the drawing, the tubing has an inlet 1 connected to the gas chromatograph column and an outlet 2 connected to the mass spectrometer. The direction of the gas flow through the tubing is indicated by arrows.

A cylindrical hollow member 3 of metal encloses two chambers 4 and 5 separated by a partition wall 6. A tube 7 of stainless steel is arranged coaxially within the'cylindrical member 3 and extends through the chambers 4 and 5 on either side of the partition wall 6. The wall of tube 7 is provided with perforations 8. A plurality of annular bodies 9 of a porous material is placed in a row within tube 7. The annular bodies 9 are separated from one another by thin annular metal washers 10. At both ends of the column formed by the bodies 9 there are placed bodies 11 of a non-porous material. The central openings in the members 9, 10 and 11 and a registering opening in the partition wall 6 form a channel 12. One end of the channel 12 is connected by a tube 13 to the inlet of the system and the other end of the channel is connected to the outlet end.

The chambers 4 and 5 are connected by exhaust tubes 14 and 15 respectively to vacuum pump means (not shown). Preferably the pump means are arranged to produce a higher degree of vacuum in chamber 5 than in chamber 4.

The device may also be provided with gas flow control means generally indicated at 16 and 17 in the figure.

When the mixture of carrier gas and carried substances is passed along channel 12 most of the carrier gas diffuses through the porous bodies 9 and enters the chambers 4 and 5 from where it is withdrawn through tubes 14 and 15. The carried substances, i.e. the gases to be analysed, do not diffuse through the bodies 9 to any large extent but are passed on to the mass spectrometer through outlet 2.

The separating eflFect and the rapidity of the separation can be increased by causing the gas stream to expand before or after it is introduced into the channel surrounded by the porous material. Such expansion can be brought about by giving the nozzle (tube 13 in'the drawing) through which the gas is introduced into the channel an appropriate form. This nozzle may also be made of a porous material. The expansion of the gas stream causes the lighter molecules of the gas mixture, i.e. the molecules of the carrier gas, to collect adjacent to wall of the channel whereby the diffusion of these molecules through the porous wall of the channel is increased. To improve the separation effect still further the gas stream can be subjected to expansion in two or more steps, the gas stream being compressed between the expansion steps.

While the principles of the invention have been described above in connection with specific apparatus, it is to be understood that this description is made only by way of example and not as a limitation of the scope of the invention.

What is claimed is:

1. A molecular separator or the like, comprising a housing; an inlet at one end of said housing and an outlet at the other end of said housing; a transverse partition in said housing dividing the space between said ends thereof into first and second chambers, said partition having a flow passage therethrough; apertured first and second conduit means respectively providing fluid communication between said inlet and one side of side flow passage and between the other side of said fiow passage and said outlet; a first adjustable valve means for regulating the flow of the gas mixture from said inlet into said first conduit means; a second valve means adjustable independently of the first valve means for regulating the flow of the mitxure through the flow passage in the transverse partition; barriers in said first and second conduit means configured to define passages for a gas mixture entering said separator through said inlet, said barriers being permeable to at least one selected gas in said mixture, whereby said gas can escape through said barriers and said apertured conduit means into said chambers whereby said gas can be separated from said mixture; and means for removing said gas from said chambers.

2. A molecular separator or the like, comprising a housing; an inlet at one end of said housing and an outlet at the other end of said housing; a transverse partition in said housing dividing the space between said ends .4 thereof into first and second chambers, said partition having a flow passage therethrough; apertured first and second conduit means respectively providing fluid communication between said inlet and one side of said flow passage and between the other side of said flow passage and said outlet; barriers in said first and second conduit means configured to define passages for a gas mixture entering said separator through said inlet, said barriers being permeable to at least one selected gas in said mixture, whereby said gas can escape through said barriers and said apertured conduit means into said chambers, whereby said gas can be separated from said mixture; means for maintaining the pressures in at least one of the first and second chambers lower than the pressure on the gas mixture flowing through the separator and for maintaining the pressure in one of said chambers lower than the pressure in the other of said chambers; and means for removing said gas from said chambers.

3. A molecular separator or the like, comprising a housing; an inlet at one end of said housing and an outlet at the other end of said housing; a transverse partition in said housing dividing the space between said ends thereof into first and second chambers, said partition having a fiow passage therethrough; apertured first and second conduit means respectively providing fluid communication between said inlet and one side of said flow passage and between the other side of said fiow passage and said outlet; barriers in said first and second conduit means configured to define passages for a gas mixture entering said separator through said inlet, said barriers being permeable to at least one selected gas in said mixture, whereby said gas can escape through said barriers and said apertured conduit means into said chambers, whereby said gas can be separated from said mixture, there being a plurality of barriers in each of said conduit means, and said barriers being separated by non-porous members; non-porous bodies adjacent the upstream barrier in the first conduit means and adjacent the downstream barrier in the second conduit means; and means for removing said gas from said chambers.

4. The separator of claim 3, wherein the barriers are fabricated of a porous material and wherein the pore size is in the range of about 10- to about 10- mm.

References Cited UNITED STATES PATENTS 1,174,631 3/1916 Snelling 55-16 2,924,630 2/1960 Fleck 55--16 3,104,960 9/1963 Chamberlin 55-158 3,239,996 3/1966 Huffman 5516 3,246,449 4/1966 Stern et a1. 5516 2,892,508 6/1959 Kohman et al. 1832 2,627,933 2/ 1953 Teter 1832 FOREIGN PATENTS 1,366,968 6/ 1964 France.

794,834 5/1958 Great Britain.

OTHER REFERENCES Mass Spectrometry of Terpenes, R. Ryhage, E. von

Sydow, in acta chem. scand 17, 1963, pp. 2025-2035.

R. Ryhage, Analytical Chemistry, vol. 36 (4), pp. 759 to 764.

RICHARD C. QUEISSER, Primary Examiner VICTOR J. T 0TH, Assistant Examiner US. Cl. X.R. 7323 .1 

